The invention of this application relates to the subject matter of concurrently filed application Ser. No. 47,842, entitled "Turbocharger Control", and filed in the name of Robert L. Cholvin.
This invention relates to devices for controlling the operation of a turbocharger. More specifically, this invention relates to a pneumatic control for controlling the rotational speed of a turbocharger turbine in response to the turbocharger compressor discharge absolute pressure.
Turbochargers in general are well known in the art, and comprise an exhaust gas driven rotating assembly for providing pressurized charge air to a combustion engine. More specifically, the turbocharger comprises a turbine rotatably driven by engine exhaust gases. The turbine is mounted on a common shaft with a compressor, and rotatably drives the compressor to supply high pressure charge air to the engine for increased power output.
In turbocharged engines, it is desirable to provide close control of the pressure, or boost level, of the charge air supplied to the engine. This is because the pressure of the charge air may, under certain operating conditions, exceed maximum pressure levels for safe engine operation. Alternately, the boost level output of the turbocharger may drop off under other operating conditions such as high altitude operation, resulting in a failure of the engine to operate at rated power. Accordingly, various turbocharger control devices have been developed seeking to prevent turbocharger overboost, while at the same time allowing engine operation under maximum rated conditions independent of altitude. See, for example, S.A.E. Technical Paper 546A, June 1962, entitled "Turbocharger Controls".
A wide variety of turbocharger controls are available throughout the prior art. Some of these prior art controls comprise so-called pressure differential-type controls wherein a control valve is operated by a diaphragm subjected to differential pressures. See, for example, U.S. Pat. Nos. 2,484,852; 4,075,849, and 4,120,156. However, these differential controls are disadvantageous in that they do not eliminate altitude sensitivity. Other turbocharger controls combine a bellows arrangement with the diaphragm to form a so-called pressure ratio control for operating a control valve. See, for example, U.S. Pat. Nos. 3,035,408; 3,102,382; 3,365,878; and 3,611,711. However, these pressure ratio controls also do not eliminate altitude sensitivity.
Some prior art turbocharger controls have been developed comprising so-called absolute pressure controls wherein a bellows arrangement is provided independently of a diaphragm for operating a control valve. See, for example, U.S. Pat. Nos. 1,816,787; 2,283,175; 2,573,231; 3,096,614; and 3,478,775. These absolute pressure controls are advantageous in that they control the turbocharger to maintain rated engine power independent of altitude. However, these prior art devices have relied for operation upon hydropneumatic systems utilizing a combination of pneumatic and hydraulic pressures. The inclusion of hydraulic fluid lines and the relatively high volume pumping requirements of an hydraulic fluid system results in a relatively expensive control scheme. Moreover, the potential leakage of the hydraulic fluid, typically high temperature engine lubricating oil, exposes the system to a substantially increased fire hazard as compared to an all-pneumatic system. Alternately, prior art absolute pressure devices have been proposed including bellows arrangements to operate a control valve independently of altitude and without the use of hydropneumatic pressure or equipment. However, these systems typically have required direct mechanical connection between the bellows arrangement and the control valve. Such mechanical connections have been found to increase system control error, as well as to introduce components subject to failure. Or, these systems have included electrical switching apparatus for coupling to the bellows arrangement, but such electrical equipment increases system fire hazard without increasing system reliability.
The invention of this application overcomes the problems and disadvantages of the prior art by providing an improved all-pneumatic absolute pressure control for turbochargers which avoids use of hydraulic fluid or components, and which substantially eliminates altitude sensitivity.